Among environmentalists and urban theorists who don’t believe societal collapse is inevitable, the prevailing wisdom dictates that high-density urban areas are the key to creating a sustainable society. Smaller housing units, walkable neighborhoods, locally produced energy and food, and access to bicycles and mass transit create a smaller carbon footprint than large homes in low-density neighborhoods and towns connected by highways. This much is known. That this formula for urban sustainability has entered the mainstream is a positive development, but it overlooks one major factor in determining livability and, indeed, the stability of society: natural resources in general, and energy in particular.

Edward Glaeser, Alex Steffen, and Geoffrey West are ardent supporters of high-density cities. Glaeser, a Harvard economist, argues for constructing skyscrapers (anathema to many environmentalists) to increase the amount of residential and commercial space in a city’s central business district. The contrast between costs of living in Chicago and New York supports this thesis. Steffen, co-founder of Worldchanging, compares high-rise buildings to tent poles that boost a city’s overall density and sustainability. He about “reweaving the urban fabric” through infill development, retrofitting, and sharable services and spaces as means of reducing the carbon intensity of the city. And West, the physicist in search of a grand unifying urban theory, offers data that shows cities create economies of scale that suburbs and small towns cannot match: city dwellers use fewer natural resources and require less infrastructure investment than their suburban and rural counterparts, and this return to scale increases as the city becomes larger. On a per capita basis, New Yorkers consume fewer resources than Chicagoans, who consume few resources than Houstonians or Cincinnatians. Furthermore, he contends that access to culture, ideas, and other people make cities natural hubs of creativity and innovation; it’s this role that make cities the linchpins of a sustainable society.

Despite the low per capita carbon footprint of city dwellers, cities consume vast amounts of resources. Sure, the world would be better off if everyone lived in Chicago-style density as opposed to, say, Atlanta-style sprawl, but the sheer size and level of activity necessarily means that cities, as a whole, will consume a large portion of the planet’s energy, water, food, and other resources. Sustainability is a word that eludes a fixed meaning, but those who think about the future of cities (whether their visions are utopian or dystopian) agree that people will need to live closer to the resources that make modern civilization possible. The post-carbon future will not allow any more places like Las Vegas or Dubai.

Not until the last century did cities manage to grow without a major body of water nearby. Desert cities in the United States, Middle East, and Asia couldn’t bloom without a major investment in infrastructure and/or desalination technology. Providing water for cities, whether you’re diverting it from a river or removing its salt content, uses a lot of energy. Coal and nuclear provide much of the world’s electricity, but coal-fired power plants and nuclear reactors cannot be in close proximity to dense urban centers. Renewable energy production, however, can and should become a common part of the urban fabric. Buildings and communities that generate their own energy, grow (at least some) of their own food, and purify their own water must become standard operating procedure if the magnificent urban future of Glaeser, Steffen, and West is to become reality.

The sustainable society is urban, and the post-carbon cities that constitute this future scenario are dense, walkable, efficient, and provide access to mass transit. But that’s not enough. In addition to being hubs of culture and innovation, these cities must also become hubs of energy production. The era of cheap and easy fossil energy is ending, but the future need not be one of downgraded technology and diminished expectation. Solar energy will be available to meet society’s needs long beyond the scope of even the most forward-looking urban plan or energy forecast. The transition to a post-carbon society will be difficult, but it’s far from impossible. Perhaps the key is to eradicate the disconnect between the places we live in and the places that make our lifestyles possible. Just as the locavore movement reconnects people to their food and the land it grows on, a local energy movement will create a connection between people and the resources upon which they depend. It’s easy to take for granted the carbon-spewing power plant or wind farm located a hundred miles outside of the city, but a neighborhood solar energy generation center would be unforgettable. It would become entrenched in the urban fabric, and it would transform the ways we think about energy and the city.